In order to evacuate a hollow workpiece the workpiece is provided with an evacuation port or outlet. The workpiece is subsequently placed in a vacuum chamber and the vacuum chamber is evacuated simultaneously evacuating the workpiece through the evacuation port. Once the chamber, and consequently the workpiece, is evacuated to the desired extent, the evacuation port must be hermetically sealed to prevent air from leaking back into the workpiece destroying the vacuum therein.
The fact that the workpiece is sealed in an evacuated vacuum chamber makes it difficult to seal the evacuation port. The chamber cannot be opened to provide access to the workpiece until the evacuation port is sealed if the vacuum is not to be destroyed. Therefore, it is necessary to seal the vacuum port while the workpiece is still sealed in the vacuum chamber. Several valves and methods are known for sealing the vacuum port while it is still sealed inside the vacuum chamber. These valves and methods all suffer from either a high rate of failure to properly seal the port or from expensive moving parts.
One such prior art method provides for a fixture that is mounted to or positioned adjacent the workpiece inside a vacuum furnace. The fixture contains a stack of ball bearings that are suspended above the evacuation port during evacuation of the furnace and the workpiece. One of the workpiece, fixture or ball bearing are provided with brazing solder. Once the chamber is sufficiently evacuated a ball bearing is dropped into the evacuation port and the furnace is heated to a temperature sufficient to melt the brazing solder and braze the ball bearing in the evacuation port atmospherically sealing the evacuation port.
The above prior art method and apparatus may be provided with a mechanism for mechanically releasing the ball bearing so that it drops into the port or the fixture may be provided with a means for releasing the ball bearing when the fixture is heated to a specific temperature. Either way, the method suffers from a high rate of failure due to any misplacement of the ball bearing or incomplete brazing. Likewise the method requires moving parts that are expensive to manufacture and susceptible to failure, particularly in view of the high temperatures involved.
The present invention strives to overcome the problems present in prior art methods and devices by providing a method and closure system for hermetically sealing an evacuation port that contains no moving parts, is inexpensive and highly reliable.